An electrical or power substation involves electricity transmission and distribution systems where voltage is transformed from high to low or the reverse using transformers. Electric power may flow through several substations between generating plant and consumer, and in the process being transformed through many voltage levels in several steps.
Appropriate equipments are selected for these functions depending on whether the substation is a transmission, sub-transmission or distribution substation. These equipments could include transformers, reactors, capacitor banks, circuit breakers, disconnector switches etcetera. Substation Automation involves protection, control, monitoring and metering functions of the above mentioned equipment and derives reliable information for efficient functioning of the substation. Currently different types of Intelligent Electronic Devices (IEDs) are used in a Substation Automation (SA) system to cater to protection, control, monitoring and metering functions of different substation equipment. The IEDs are microprocessor-based controllers of power system equipment, such as circuit breakers, transformers, and capacitor banks. Typically, the IEDs receive data from sensors and power equipment, and can issue control commands, such as tripping circuit breakers if they sense voltage, current, or frequency anomalies, or raise/lower voltage levels in order to maintain the desired level. Common types of IEDs include protective relaying devices, load tap changer controllers, circuit breaker controllers, capacitor bank switches, recloser controllers, voltage regulators, etc. These IEDs are advantageous because, with the available microprocessor technology a single unit can perform several protection, metering, monitoring and control functions concurrently.
Substation Automation forms an important and complex aspect for maintenance and control of different equipments involved in different processes within the substation. The IEDs deployed in SA systems use communication protocols to communicate substation equipment data to each other. Multiple protocols exist for Substation Automation, which include many proprietary protocols with custom communication links However, interoperation of devices from different vendors is highly desired for simplicity in implementation and use of Substation Automation devices.
The IEC61850 standard from International Electrotechnical Commission (IEC) is a standard for communication networks and systems in substation, which advocates interoperability amongst Intelligent Electronic Devices (IEDs) from various manufacturers using common engineering models, data formats and communication protocol. Recent IEDs are designed to support the IEC61850 standard for substation automation by implementing the IEC61850 profiles as per the application requirements, thereby providing interoperability and advanced communications capabilities and these IEDs are termed as IEC61850 compliant IEDs. Hereinafter the term IED should be interpreted as IEC61850 compliant IED unless specified otherwise.
IEC 61850 features include data modeling where complete functionality of the substation is modeled into IEC61850 logical nodes (LN) that are grouped and arranged under different logical devices (LD). Logical nodes are the smallest part of a device model that represents a function in an IED. The data published by this function are represented as data objects under these LNs. Logical devices are virtual devices that exist to enable aggregation of logical nodes, data sets and control blocks for communication purposes.
The IEC61850 based IEDs currently support only the fixed number of preconfigured Logical Nodes out of the available Logical Nodes in IEC61850 standard based on the fixed number of physical inputs from associated power system equipment. The preconfigured Logical Nodes described herein above mean that few of the IEC61850 Logical Nodes are implemented in the IED based on its physical capability, real-world application support and the common understanding with the IED application configuration tool. This puts a limitation on expandability of these IED configurations with respect to IEC61850. Further, the bay level functionality extension is not possible with the existing devices as there are physical IOs and IEC61850 logical nodes insufficiency. The functionality extension is defined herein as extending the real world application/function performed by the IED dynamically based on its physical capability.
For example, a substation has an IEC61850 compliant IED that supports only a LN of class GGIO (logical node pertaining to Generic Input Outputs). In future, the substation requires transferring of various signals like Temperature Alarm, Pressure Alarm etc. to a control station. For being capable of doing this the IED should also support SIMG (represents Insulated Medium Supervision for Gas) logical node class as well dynamically (Enabling the related functional block, logical nodes, etc., during reconfiguration using the IED application configuration tool), which is not available in the current IEDs and IED configuration tools.
The current IEDs do not support adaptive reconfiguration (configuring an IED functionalities as per the real-world application requirements) of the IEC61850 data model and hence a need such as extension of the data objects in the logical nodes cannot not be fulfilled. Data object extension referred herein means aggregating the various number of data objects to group multiple binary input/output in a logical node. The data models in IEC61850 are used for description of the information produced and consumed by applications and for the exchange of information with other IEDs.
Therefore there is a need for flexibility in configuration of the IEC61850 data model in IEDs to support variations in information emanating from them like physical inputs, application function outputs that cannot be defined apriori. This adaptation implies a variable number of Data Objects, typically one per information element, in one or plurality of Logical Nodes in IEDs to suit the user or substation requirement.